1. Field of the Invention
The present invention relates to a tractor. Particularly, it relates to a power train system, an attachment lifting system, and a traveling control system in a tractor.
2. Background Art
According to the most popular conventional layout in tractors, a frame at a front portion of a tractor supports an engine. Behind the engine the frame supports a transmission. A seat is arranged above the transmission. The power of the engine is transferred to the transmission in order to drive the rear wheels. Many popular rising tractors employ this layout because it is advantageous in securing a compact arrangement of a power source and power train.
In such a tractor, the seat may be lowered as much as possible for getting on and off and for lowering the center of gravity, while the seat is necessarily disposed above the transmission. However, when the transmission is entirely lowered, an input shaft of the transmission becomes lower than an output shaft of the engine. The vertical difference between the output shaft of the engine and the input shaft of the transmission complicates the power train part between the engine and the transmission. Furthermore, this power train part between the engine and the transmission, which is disposed between the feet of an operator, must be compact and laterally narrow so as to secure a sufficient foot space for the operator. If the seat can be lowered, there arises the problem that the operator is liable to feel a strong vibration from the engine.
Next, the above-mentioned tractor usually comprises a hydraulic lift device disposed at the rear end of the tractor for raising and lowering working attachments. A hydraulic pump for feeding pressure-oil to the hydraulic lift device is conventionally provided on the transmission. The power for driving the hydraulic pump is taken out from the driving power in the transmission.
A certain amount of oil discharged by the hydraulic pump must be secured for lifting the working attachment. Therefore, the driving power for the hydraulic pump must be taken out from the upstream of transmission gears and clutches in the transmission. The transmission for driving the rear drive wheels and a rear-PTO shaft is provided at the front portion thereof with an input shaft for receiving power from the engine before the transmission. Thus, for simplifying a drive train to the hydraulic pump, the hydraulic pump is desired to be as near as possible to the input shaft at the front end of the tractor. However, for shortening oil piping between the hydraulic lift device as an oil source and the hydraulic pump and for reducing the loss of hydraulic pressure loss, the hydraulic pump is desired to be near the hydraulic lift device on the rear end of the tractor. Consequently, there are two requests contradictory to each other about the arrangement of the hydraulic pump for lifting the rear working attachment.
Furthermore, as being well-known, some of the tractors, e.g., agricultural tractors, have continuously variable transmissions, whose speed reduction ratio is varied by a speed-change operation tool such as a lever or a pedal to be operated by an operator sitting on the seat. It would be convenient for an operator getting off the tractor to operate such a speed-change operation tool to vary the speed reduction ratio of the continuously variable transmission while handling a steering wheel, for example, when the tractor must travel on a steep slope where it may be unbalanced. If the speed-change operation tool is a pedal, it is out of the question while the operator is off the tractor. A lever as the speed-change operation tool is conventionally provided beside the seat, where the operator sitting on the seat can easily handle the lever and the interlock system between the lever and the transmission can be simplified. However, it is difficult to be operated by an operator standing beside the tractor.
If the speed-change operation lever is disposed on a side of a dashboard, an operator standing beside the tractor can easily operate the lever while handling the steering wheel. However, such a speed-change operation lever is arranged from the continuously variable transmission which is longitudinally intermediately disposed in the power train between the engine and the rear drive wheels. Thus, the problem arises how the linkage between the lever and the transmission is arranged compactly without complexity. Furthermore, this linkage must be disposed so as to be prevented from hindering a steering device for turning steerable wheels according to the operation of the steering wheel.
A tractor according to the present invention comprises a vehicle frame, an engine including a flywheel, and a first vibration isolator through which the engine is supported by the vehicle frame, a transmission including an input shaft and a housing, wherein the input shaft is disposed at an upper portion of the housing and lower than a rotary axis of the flywheel. A pair of first and second universal joints are interposed between the flywheel and the input shaft, the first universal joint being nearer to the flywheel than the second universal joint. A second vibration isolator is interposed at least either between the flywheel and the first universal joint or between the input shaft and second universal joint.
Consequently, the transmission can be entirely disposed at a low position in the tractor, thereby desirably lowering a seat to be disposed above the transmission so as to ease an operator to get on and off the tractor. Also, the center of the weight of the tractor can be lowered so as to balance the tractor suitably, thereby stabilizing the tractor in traveling.
The driving connection between the flywheel of the engine and the input shaft of the transmission using the universal joints is simple and economical compared to using bevel gears or the like. Also, this driving connection system, disposed between the feet of an operator sitting on the seat, is compact so as to secure a sufficient and comfortable foot space for the operator.
Although the operator sitting on the lowered seat is close to the engine the first vibration isolator supporting the engine comfortably restricts the engine vibration to be transmitted to the seat.
The second vibration isolator, which is preferably interposed between the flywheel and the first universal joint, efficiently reduces a torque variation caused in the flywheel of the engine before the torque variation is transmitted to the transmission, thereby reducing the sound generated between gears in the transmission by the torque variation.
The second vibration isolator is disposed so as to make the primary and final transmission ends thereof coaxial with each other.
In addition, a hydrostatic transmission is encased in a transmissing housing with a distributing drive gear whose input shaft is provided thereon. A main PTO drive shaft is disposed in the transmission housing so as to be offset from the input shaft, and a PTO clutch is provided on the main PTO drive shaft so as to engage or disengage the main PTO drive shaft with a PTO shaft. A primary gear of the PTO clutch meshes with the distributing drive gear on one side of the distributing drive gear. A hydraulic pump other than the hydrostatic transmission is provided outside the housing. A gear for driving the hydraulic pump meshes with the distributing drive gear on the other side of the distributing drive gear.
The output gear provided on the input shaft shares the power between the hydraulic pump and the PTO drive train. Thus, a constant amount of oil discharged from the hydraulic pump is held while the constant rotation of the engine is performed.
The output gear together with the hydraulic pump connected to it can approach the rear end of the tractor so as to shorten oil piping between the hydraulic lift device and the hydraulic pump.
The opposite arrangement of the primary gear of the PTO clutch and the gear for driving the hydraulic pump with respect to the output gear simplifies the drive train to the hydraulic pump. Meanwhile the drive train is prevented from hindering the PTO clutch on the PTO drive train, thereby contributing to the compactness of the tractor.
The PTO transmission shaft drivingly connecting the PTO drive main shaft with the PTO shaft through gears is disposed coaxially with the input shaft of the transmission, thereby enabling the lateral and vertical width of the transmission to be reduced. Consequently, the tractor can be laterally compact and provided with a sufficient minimum clearance above ground.
The tractor according to the present invention comprises a continuously variable transmission including a control arm for changing a speed reduction ratio in the continuously variable transmission. A steering wheel shaft is relatively rotatably held in the steering column in a dashboard. A steering wheel is fixed onto a top of a steering wheel shaft so as to be disposed above the dashboard. A substantially vertical speed-change operation shaft, which interlocks with the control arm and is rotatable around an axis thereof, is disposed beside the steering column in one of left and right sides of the tractor. The dashboard is provided at a lateral side surface thereof with an opening. A speed-change lever having a base portion and a grip portion opposite to each other is passed in a lateral direction of the tractor through the opening of the dashboard so as to project the grip portion laterally outward from the dashboard. The base portion of the speed-change operation shaft is connected to the speed-change lever in the dashboard.
An operator beside the dashboard of the tractor can walk along side the tractor while handling the grip portion of the speed-change lever and the steering wheel. The vertical speed-change operation shaft, constituting a speed-change control device and the steering column are compactly disposed so as to secure a large free space for other parts in their vicinity while they being prevented from hindering each other. By suitably locating the top of the speed-change operation shaft, the height of the speed-change lever can be located at an optimal position for being handled by the operator beside the tractor.
Furthermore, a bottom portion of said steering column is disposed above a transmission shaft interposed between an engine and the continuously variable transmission. A steering system including an input shaft is interposed between the steering wheel shaft and steerable wheels so as to laterally turn the steerable wheels according to the handling of the steering wheel. The steering system is disposed in the other of left and right sides of the tractor laterally opposite to the speed-change operation shaft. A flexible joint connects a bottom portion of the steering wheel shaft to the input shaft of the steering system.
While the transmission shaft is disposed just under the bottom portion of the steering column, the input shaft of the steering system, connected to the bottom portion of the steering wheel column through the flexible joint, can be slanted, thereby being prevented from hindering the transmission shaft. The speed-change operation lever and the steering system are compactly disposed laterally opposite to each other. Thus, all the drive train between the engine and the continuously variable transmission, the steering system and the speed-change control device can be easily disposed compactly in a restricted space, e.g., in the dashboard.
Furthermore, the tractor is provided with a neutral pedal and an interlocking mechanism that forcedly puts the continuously variable transmission into neutral and disengages the PTO clutch according to treading of the neutral pedal.
An operator can select either the speed-change lever or the neutral pedal to be operated for stopping the tractor. The neutral pedal is available for an operator""s operation of the tractor because only one tread thereof disengages the PTO clutch.
Furthermore, if the continuously variable transmission is a hydrostatic transmission (hereinafter referred to as an xe2x80x9cHSTxe2x80x9d), a closed fluid circuit thereof is bypassed by the treading of the neutral pedal.
An HST is advantageous in its smoothly continuous variation of output rotational speed and direction by operation of only the speed-change without a complex linkage. The HST is also advantageous in its braking function when it is set to neutral, thereby enabling a vehicle (the tractor) to stop without a mechanical brake. However, the neutral position of the HST is difficult to adjust. An error is liable to be generated in the neutral setting of the HST or in the linkage between the speed-change lever and the control arm. Such an error causes a vehicle to travel slowly while the speed-change lever is set at the neutral position. The above bypass construction in the HST solves this problem. That is, by treading the neutral pedal, the closed fluid circuit of the HST is bypassed so as to cancel the drive of the HST, thereby stopping the tractor.
The base portion of the speed-change lever and the top of the speed-change operation shaft are connected through a flexible joint. A guide slot for forward drive and a guide slot for backward drive are joined to each other so as to be cranked, thereby constituting the opening of the dashboard.
Accordingly, the speed-change lever, when it is shifted through the cranked opening between its forward drive position and its backward drive position, must be once located in a vertical slot and moved vertically. Even if the operator unexpectedly touches the speed-change lever, the worst situation that the traveling direction of the tractor will not accidentally reverse. The operational direction of the speed-change lever for forward and backward driving can be learned so as to facilitate the operation of the tractor. The flexible joint interposed between the base portion of the speed-change lever and the top of the speed-change operation shaft is disposed in the dashboard so as to be protected from dust or the like, thereby being secured in its durability.
A fuel tank is disposed in the dashboard before the steering column. The fuel tank is provided at its upper portion with a recess through which the speed-change operation shaft is allowed to pass.
The arrangement of the fuel tank in the dashboard contributes to the compactness of the tractor. The space below the speed-change lever can be applied for the fuel tank, thereby securing the required volume of the fuel tank while preventing the fuel tank from hindering the speed-change lever.
Other and further objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and drawings.